High-frequency variable inductance



Nov- 9, 1948. J. BOWERS 2,453,113

Hmn-FRE uEucY VARIABLE INDUCTANCE Filed Dec. 6, 1944 2 Sheets-Sheet 1Nov. 9, 1948. J. L. BOWERS ,1 3 I HIGH-FREQUENCY VARIABLE INDUCTANCEFiled 090. 6, 1944 2 Sheets-Sheet 2 Q/VZ/M'W $AA Patented Nov. 9, 1948HIGH-FREQUEN CY VARIABLE INDUCTANCE Jack L. Bowers, Dayton, Ohio,asslgnorto the United States of America as represented by the Secretaryof War Application December 6, 1944, Serial No. 586,935

6 Claims.

(Granted under the act of March 3, 1883, as

amended April 3, 1928; 370 O. G. '15'!) The invention described hereinmay be manufactured and used by or for the Government for governmentalpurposes, without thepayment to me of any royalty thereon.

The invention to be hereinafter described relates to a variableinductance adapted to be used as a tuning element in a high frequencyradio circuit.

Heretofore difilculty has been experienced in removing (electrically)the unused portion of an inductance, due to the character of very highfrequency currents.

Furthermore, it has been common practice to tune the capacitor ratherthan the inductance because of the above difllculty.

The only common method of tuning inductance uses a singleroller'contacting only a single helix at a single point as it travelsthe coil. That method does nothing to remove the electrical effect ofthe by-passed helices. I

The main objects of the present invention are to completely eliminate orgreatly minimize the above and other objections and provide a simple andemcient variable inductance in which-the by-passed helices of the coilwill definitely, reliably and permanently be removed as far aselectrical effect is concerned.

' In.order to more clearly disclose the construc tion, operation and useof the invention, reference should be had to the accompanying drawingsforming part of the present application.

Throughout the several figures of the drawings like reference charactersdesignate the same parts in the different views.

In the drawings:

Figure 1 is a front view of the invention;

Figure 2 is a top plan view;

Figure 3 is an enlarged end view of one coil assembly in operativeposition, showing connection of slug to coil; and v Figure 4 is anenlarged fragmentary cross section through one of the connections shownin Figure 3.

Referring to the drawings in detail, the variable inductance comprises acoil A, two being shown in the particular arrangement illustrated,suitably mounted on ceramic or other insulating blocks or supports B andreciprocably receiving cylindrical slugs C of suitable conductingmaterial.

In order to definitely and reliably short out remove, electricallyspeaking. the unused portion of an inductance, usually helices of acoil, the movable member such as the slug C in this case, must remaineither in actual contact with the coil member or so close thereto as tocause no more than negligible impedance to high frequency currents.

In the present invention the coils are shown as cylindrical. The slugs Care of substantially havin approximately the same lengths as the coil,preferably somewhat longer. They are slightly less in outside diameterthan the inside diameter of their respective coils. This differenceshould be sufllcient to enable the slug to both rotate within and travelfreely longitudinally through its respective coil, without actualcontact with said coil. That permits movement'of the slug within andthrough the coil without friction due to contact. At the same time, itmaintains the radial distance between the coil and slug at a point wherethe impedance to high frequency currents will be only negligible. Italso assures a continuous slug surface in close proximity to the coilthroughout the length of that portion of the slug within the coil.

In the present instance the invention is shown as coupled with amagnetron type oscillator of known construction. In such relation it isused as the inductive portion of a tuned circuit, in which thecapacitance is derived from the distributed capacitance of the magnetrontube and the inductance itself. To obtain lower operating frequenciesadditional ilxed capacitance may be added in parallel with theinductances, in well known manner.

In the present preferred arrangement, a shaft i extends axially throughthe aligned coils A and the slugs C are slidably and revolubly mountedon that shaft, either directly on it or indirectly on it. Each slug isconnected by a pair of rods 2 with a toothed disc. plate or large gear 3mounted on shaft I. One gear 3 is driven through a suitable gear train,by hand or by any other suitable and acceptable means. The other gearwill be driven by a counter shaft 4 and intermeshed smaller gears 5. Inthe present instance, the gear drive is so proportioned as to travel thetwo slugs C at the same rate. a

The longitudinal travel of each slug is effected in the same way and bythe same devices. A description of one set of such devices will,accordingly, cover both. A preferred arrangement is to provide theinner, forward or lead end of the slug with radially extending smallyokes 6 semi-circular concave seats or sockets which, in operativeposition, fit about, embrace and receive the conductor rod, wire or tubeof coil A. Yokes 6 are slidably mounted in blocks 6' extending radiallyfrom the respective slug and provided with radial socket I for freelyslidably receiving yoke 6. A yieldingly compressible device such as acoil spring 8 confined in socket 1 between yoke 8 and block 6continuously maintains sliding contact between coil A and yoke 6. .Asshown, and as preferred,

three such yokes are used at the respective end of each slug and thoseof each slug are equally spaced circumferentially, providing asubstantially continuous contact, electrically, throughout therespective helix. With .both slugs thus slidessence ably connected totheir respective coils, rotation of the slugs by the above drive compelscorresponding atrial or longitudlnel trovel of them relative to theirrespective coils with correspond ing variation of inductance. Reversedrive eiiects reverse travel. This construction and op eration maizepossible regular, continuous, pro= gressive and uniform travel or icedoi the slug. Preferably a wiping contact 9 is provided on one of theyoite blocks 6 associcted with each slug if), this electrical contactslidlngly engaging shoit 0. Due to the forward position of each contact9 with respect to its slug 2 this reduces the elec trical path betweenthe slug contacts of the re-= spective coils. This permits operation athigher frequencies than would otherwise be possible with the sameequipment. While two coils and slugs have been shown, it will be wellunderstood that one only or more than two may be used and are equallywithin the invention.

Likewise, three equally spaced connections between slug and coil havebeen stated as preferred. Any number of such connections from one up maybe used but three equally spaced have been found highly satisfactory.Also, grooved rollers instead of yolzes 6 have been found verypractical. Many other connections may be used provided they nose theslugs to follow the spiral of the coil in substantially the same way.For instance, the slugs could be formed with spirally disposed ribs tofit between the helices of the coils so that when rotated the slugswould have the same oction and movement as a screw bein turned into itsbore or socket. That, howevea, is undesirable because of the high degreeof friction it would involve. Likewise, in cases where more then onecoil and slug are used, the slugs need not be operated at the some ratesbut may be operated at different rates may best suit the respectivecircum stances.

Although the coil and slug have been referred to and shown as a slugwithin a coil, it hardly need be stated that the relation, in thatrespect, may be reversed: i. e., the slug element may be outside and thecoil inside, end there may be a considerable variation in that relativeassembly also. in. all cases, the close relative, radial posi= tlons fthe parts must be maintained, however, to avoid more than negligibleimpedance to high frequency currents.

lit is thought that the construction, operation and use of the inventionwill be clear from the preceding detailed description.

Changes may be made in the construction, orrangement and disposition ofvarious features of the invention, within the scope of the appendedclaims without departing from the field of the invention and it is meantto include all such with in this application, wherein only one preferredterm has been illustrated purely by way or ex= ample and with no thoughtor intent of, in any degree, limiting the invention thereby,

Having thus described my invention, what 1 claim and desire to protectby Letters Patent is:

1. A variable inductance for high frequency radio circuits comprising acoil, means for supporting said coil in a fixed position, anelectrically conductive slug element movable longitudinally relativelyto said coil, means for moving said slug element, a plurality of blockscarried by and extending radially from said slug and provided with yokereceiving sockets, coil engaging and 101- lowing yokes reclprocable insaid sockets and means within said sockets engaging said yokesyieldingly maintaining the same in operative engagement with theaforesaid coil.

2. A variable inductance for high frequency radio circuits comprising acoil, means for supporting said coil in a fixed position, anelectrically conductive slug element movable longitudinally relativelyto said coil and having a diameter sufil cicritly large to rendernegligible the impedance to high frequency currents, means for movingsaid slug element, a plurality of blocks carried circumferentiallysoul-distantly distributed by said slug and extending radially therefromsaid blocks being provided with yoke receiving sockets, a coil engagingand following yoke reciprocable in each said soclret and means withineach said socket engaging the respective yoke and yieldingly maintainingthe same in operative engagement with the aforesaid coil.

3. A variable inductance for high frequency radio circuits comprising aplurality of coils,

I means for supporting said coils in fixed positions,

an electrically conductive slug element movable longitudinallyrelatively to each of said coils and having a diameter sufficientlylarge to render negligible the impedance to high frequency currents, aplurality of blocks carried by and extending radially from each of saidslugs and provided with a yoke receiving socket, coil engaging andfollowing yoires reciprocable in said sockets, means within said socketsengaging said yoites I yleldlngly maintainin the same in operative engagement with the aforesaid coil and means for moving said slug elementssynchronously.

t. in combination, an inductance coil, an electrically conductive slugclosely fitting adjacent the convoiutions of said coil to rendernegligible lid the impedance thereof to high frequency currents, meansassociated with said slug forming eieccm-mechanical connection to saidcoil, and means for longitudinally adjusting said slu relative to saidcoil.

5. A variable inductance comprising a coil, an electrically conductiveslug element revolubly and longitudinally movable relative to said celland closely fitting adjacent the convolutions of said coil to rendernegligible the impedance thereof to high frequency currents, andelectrical contact means associated with said slug element slidably hosing said cell,

6. A variable inductance comprising in combination a pair of coils, anelectrically conductive slug associated with each coil, each slugclosely fitting adjacent the convolutions of its respective coil torender negligible the impedance thereof to high frequency currents, anelectrically conductive shaft extending longitudinally of said coils andsupporting said. slugs for rotation, electrically conductive meansassociated with each said slug slidably engaging the corresponding coil,and. an electrical contact fixed to each said means and slidablyengaging said shaft.

JACK L. BOWERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,690,228 Heising Nov. 6, 19281,818,316 Gebhard Aug. 11, 1931 1,831,375 Adams Nov. 10, 1931 1,860,722Rudolph et a1 May 31, 1932 2,226,822 Kirk et a1 Dec, 31, 1940 2,324,189Bock July 13, 1943

